Extractive distillation of hydrazine with a glycol



May 11, 1954 B. HjNlcoLAlsEN 2,578,298

EXTRACTIVE DISTILLATION OF' HYDRAZINE WITH A GLYCOL Filed Nov. l5, 1952 Ber'nord H. Nicoloisen INVENTOR Patented May 11, 1954 .EXTRACTIVfE fDISTILLAT-IQN F.;HYDRA VAZINE WITH A vGLYCOL Bernard-H. Niclnisen, Lcyvistonf-NgY., assigner to 'Mathieson Chemical Corporation, fa, corpo- Applcation-Noyember 15 1952, .Seria-ENQ. '320,689

My invention relates v'toagprocess for the production of substantially anhydrous hydrazine 'from rdilute aqueous "hydrazine solutions byex- E-tra'ctive distillation In the Raschig Vsynthesis hydrazine .obtained `asf-an extremely diluteaqueous solution (about f1^to "3 'per cent) by distillation 4.of 'the .reaction mixture. yAnhydrous 'hydraz'ine .has tbeen ojb- :taine'd lfrom `.the dilute Vsolution usually A"by one o'ftwo :general methods. Tn one ugroup of methods, the 'base maybe 'absorbed in acid, the .salt 'separated from "water 'and ammonlyzed to obtain lanhydrous `hydrazine in liquid ammonia. The latter is readily removed vto obtain `the anhydrous hydrazine product. `In another group of processes for 'the Isame purpose, 'the dilute aqueous hydrazine `may be "fractionated at atmos- .pheric pressure ,to cbtain :concentrations/up to Athe azeotropic vcomposition containing "71.15 per cent ohydrazine. "Further distillation at latmospheric pressure does not serve 'toincrea'se 'theconcentration ofhydrazin'e. "The resulting so-called hydrazine hydrate may bedistill'ed `from caustic soda or other valkalies, usually by multiple dis- 'til-lation, vin order to .obtain 'anhydrous ,hydraz'ine "Iheseprocesses are expensive `and appreciable hydrazine loss .occurs "by decomposition .on v`heatingever Aextended. periods.

Ihavefound that dilute Aaqueous hydrazine can be gcenc'entrated by extractive .distillation in 'the presenceof a glycol as a solvent. I:Substantially anhydrous 'hydrazine can 'be produced by 'establisli'ing'fconditions of extractiva :distillation 'psuc'h that' the water is vaporizedffromthe"distillation zone while the glycolandsubstantially anhydrous hydrazine plus minor proportions o'f water are removed asf-the liquidbottoms Whichiare then distilled torecover glycol and to Vaporize substantially llanlxydrous hydrazinefeg. about 95'iperacent .hydrazine @Myprocess is particularlysadvantagenus that the anhydrous .hydrazine product is recovered as van overhead product. I have found that ethylene "glycol-is'especially advantageous an extractivexsolyent for the -.distillafOtlfrer .glycolslsuch-aspropy1'ene glycol, sbutylene glycols and diethylene glycols are also use ful.

The preferred charge stock for the present invention is hydrazine hydrate or a composition approximating that concentration obtained usually by the atmospheric fractionation of more dilute aqueous hydrazine at atmospheric pressure. Preferably the charge tothe process of the present invention contains at least about 60 per cent of hydrazine and not over about 40 per cent 2 .of Water. Such chargestocks lare readily ob- 'tainedbyatmospheric fractionation. Moredilute aqueous solutions of hydrazine imay be used.

.According to the present invention vrsuitable vhydraitine hydrate solutions as Idescribed aboye are icharged with recycled and "make-*up glycol to an extractive fractionatirrg column. The glycol is introducednear thetop 'of the 'column and *the raqueous hydraz'ine ,at any "suitable lpoint Vbut prefierably 'not above 'the ,glycol inlet. The column 'is operated under conditions of Aextractive distilla- "tion including elevated *temperature -*with vcor-relative pressure -andv sol-vent-to-chargeratio estab- `lishing separation 'of a nvapor fraction comprising `substantiaily'pure water'and Aa vliquid Ii-raction comprising `glycol and hydrazine With-minor proportions of water. excess AVof glycol to charge, zpreferably -in countercurrent contact, Vis employed. 'Sui-table proportion-s -of glycol to hydrazine Tlhydrate on a vmolar-basis vary 'from about 1`525to 4 to fl.

Heat vvis conveniently lintroduced tinto v:the botftom V'of the column 'by-means Lof a reboiler. 'Substantiallypure wateris taken overhead. The top temperature is thereforesubstantially -1f00 -`C. at

"sea-level atmospheric pressure or correspondingly 'lower temperatures at @lower pressures. The bottoms from fthe extractivefco'lumn comprise pri-nvcipallyglycol and hydrazinelin the molar proportions of `about 255 :'-1 to 11 z 1 ltogether with minor proportions of AWater --not usually exceeding about 1.0;1 mole permole vof hydrazine. Since all -of the water in these 'bottoms appears in -ithe final 'hydrazine'product the temperature control :at =this point is very importantand Lthis vtermJeratur-e 4shouldfbe maintained Within a 'narrow range. "HoWever, this 'range-maybe 'between about `1670 and '19.0 depending .on theratio of glycol to hydraz'ine .hydrate "feed Higher proportions "of glycol produce correspondingly higher ,bottom .temperatures in .the `extractiye A.columnsinco the composition s ,richer .the Vhigher `boiling .glycol component. Y Y y The rbottoms from the 'extractive column are .athenicharged ytto ashydraz'inetillfmhim ,visahea'ted by means of a reboiler, to separate the hydrazine from the glycol. The temperature is controlled so that hydrazine is vaporized overhead and glycol is recovered as bottoms. The bottoms from the still, comprising substantially anhydrous glycol and about 1 to 10 per cent of hydrazine,

through a reflux system and obtained as an overhead product.

My invention will be further illustrated by the simplified flow plan of the accompanying drawing. In the illustrated flow, a dilute aqueous hydrazine stream from the synthesis reaction is charged by means of connection -i to hydrate still Il. Distillation is effected by means of reboiler i3. Hydrazine hydrate is withdrawn as bottoms through connection l2 to reboiler i3. Reciroulation to the bottom of still Il through vapor return line I4 maintains a still bottom temperature of about 122 C., for example. rEhe still top temperature is 100 C. at sea levelatmospheric pressure and water vapor is taken overhead through connection l5 and condenser system I6. Reflux may be returned to the top of the still through connection l1 while the net water removed is Withdrawn through connection I8.

The hydrazine hydrate produced is withdrawn from reboiler i3 through line i9 and is charged to extractive still 20. Glycol, for example, ethylene glycol, comprising recycle material from line 2l and make-up material added by connection 22 is introduced to an upper portion of extractive still by means of connection 23. A still bottom temperature of about 160-190 C. is maintained by recirculating bottoms through line 24, reboiler 25 and return line 26. stream is taken overhead through connection 27 and condenser system 28. Reflux may be returned to the top of the still through connection 29 While vthe net water removed is withdrawn through connection 30. The still top temperature is 100 C. at seat level atmospheric pressure. The bottoms from the extractive still 20 consisting substantially of glycol, hydrazine and a minor proportion of water are removed from reboiler 25 through line 3l to the hydrazine still The still is heated 32 to separate hydrazine. by circulation of glycol bottoms through line 33 to reboiler 34 equipped With return line 35 and the temperature is controlled so that hydrazine is vaporized overhead and glycol is recovered as bottoms. The bottom product stream, comprising substantially anhydrous glycol and about 1 to 10 per cent of hydrazine, is recycled by means of line 2| from reboiler 34 to extractive still 20. A vapor stream consisting of substantially anhydrous hydrazine, e. g. at least 95 per cent, is taken overhead by line 36 through a reux system 31. Reflux may be returned to the still by line 38 and the anhydrous hydrazine product is removed by line 39.

In the hydrazine column, nitrogen or other inert gas is preferably introduced as a blanket to prevent'access of air to the anhydrous hydrazine condensate. Suitable inert gases for this purpose include nitrogen, helium, sulfur hexafluoride and the like.

The process of my invention Will be further illustrated by the/following examples:

l l Eample I A feedl having the following composition in A Water vapor I -ture o .99 C. and a pressure of 740 imm. Hg. lThe distillate comprised in per cent by weight:

hydrazine 0.04, water 96.7, ethylene glycol 0.00, and ammonia 3.3. The bottom liquor was maintained ata temperature of 160 to 162 C. A

portion continuously withdrawn from the column reboiler had the following composition in per cent by weight: hydrazine 17.2, Water 1.0, ethylene glycol 81.8, and ammonia 0.00.

Thus no signiicant loss of ihydrazine occurred in the distillation by carry-over and the residual product had a composition corresponding to about 95per cent hydrazine based on the hydrazine and Water contained therein.

"Example II 'extractive distillation tower.

I claim: v

1. A process for the production of substantially anhydrous hydrazine from aqueous hydrazine which comprises subjecting the aqueous hydrazine charge to extractive distillaiton with a glycol solvent under extractive distillation conditions or elevated temperature, pressure and solventto-oharge ratio establishing separation of a vapor fraction comprising substantially pure Water and a liquid fraction comprising glycol and I., hydrazine substantially free from Water, removing and distilling the liquid fraction to .recover a vapor fraction comprising substantially anhydrous hydrazine and a liquid fraction comprising glycol solvent.

2. The process of claim 1 in which the glycol is ethylene glycol.

3. The process of claim 1 in which the liquid fraction comprising glycol solvent is returned to the extractive distillation step. v

References cited in the me of this patent UNITED sTATEs PATENTS 563,164 Great Britain Aug. 1, 1944 

1. A PROCESS FOR THE PRODUCTION OF SUBSTANTIALLY ANHYDROUS HYDRAZINE FROM AQUEOUS HYDRAZINE WHICH COMPRISES SUBJECTING THE AQUEOUS HYDRAZINE CHARGE TO EXTRACTIVE DISTILLATION WITH A GLYCOL SOLVENT UNDER EXTRACTIVE DISTILLATION CONDITIONS OF ELEVATED TEMPERATURE, PRESSURE AND SOLVENTTO-CHARGE RATIO ESTABLISHING SEPARATION OF A VAPOR FRACTION COMPRISING SUBSTANTIALLY PURE WATER AND A LIQUID FRACTION COMPRISING GLYCOL AND HYDRAZINE SUBSTANTIALLY FREE FROM WATER, REMOVING AND DISTILLING THE LIQUID FRACTION TO RECOVER A VAPOR FRACTION COMPRISING SUBSTANTIALLY ANHYDROUS HYDRAZINE AND A LIQUID FRACTION COMPRISING GLYCOL SOLVENT. 